1. Field of The Invention
The present invention relates to electronic temperature and coolant level monitors suitable for use with an internal combustion engine.
2. Background Art
A number of devices have been disclosed in the art, which devices are intended to monitor temperature and coolant levels in vehicular engines, as disclosed, for example, in U.S. Pat. Nos. 4,672,920, 4,381,744, 3,832,982 and 3,694,804.
Such prior devices, however, generally exhibit one or more notable shortcomings. For example, at least some prior devices, designed to monitor car engine temperature so as to provide a warning when an excessive engine temperature is reached, fail to provide adequate warning before engine damage occurs. More specifically, in some prior devices the gages and light indicators in a vehicle are designed to indicate the heat of the coolant in the engine by communicating with a heat sensor that is in contact with the engine coolant. When the coolant overheats, the light may come on or the gage may move into its warning area but, if the driver doesn't notice it at that point, the coolant becomes hotter until it builds up a tremendous pressure and finally empties out of the engine by either bursting a hose or backing into a reserve tank. Once this happens the indicator no longer provides a true reading because of the sensor's loss of contact with the hot coolant and, as the driver continues to operate the vehicle, outside air cools the engine surface where the sensor is located. Meanwhile the center of the engine becomes even hotter. It is only when the engine gets to the point where it begins to vibrate that the driver first receives his or her indication that an adverse condition has occurred. Because the dash indicators may still be reading close to normal levels even at this point, the driver may continue to drive until the motor finally stops running.
Some prior devices have sought to overcome this problem by means of devices that monitor the pressure of the coolant, i.e., such that a pressure above a selected level indicates an overheated engine. This method may not work satisfactorily, however, in a cooling system that incorporates an overflow tank, as most vehicles now do, because the cooling system does not maintain constant pressure.
Other devices are designed to shut the engine down when it overheats. Aside from the fact that this may not be a safe warning method, the device may not trigger such action soon enough. Every individual engine operates at a different temperature which may be drastically affected by the age and condition of the engine and cooling system. Therefore, it is necessary for the factory preset temperature to be at a high enough setting to avoid triggering the shutdown device unnecessarily. Consequently, such a warning device may not be sensitive enough to shut the engine down soon enough before costly damage is done.
Further problems can be presented with devices that measure temperature of coolant fluid when a leak develops in the bottom hose of the coolant system, i.e. the intake hose of the system. Since the coolant system is intended to be maintained under a reduced pressure, a leak in this hose could result in air being absorbed into the coolant system and, more specifically, air being absorbed by the coolant. This will result in decreased heat transfer capabilities of the coolant which, in turn, can result in a temperature reading that does not accurately reflect the heat of the engine.
Further, in addressing the problem of monitoring the coolant level in an internal combustion engine, it should be noted that mechanical devices are usually not satisfactory for such purpose because of the constant motion of the coolant during operation of the vehicle. Such problem is particularly annoying when incorporating an audible alarm into the system.
Certain prior devices consist of a single probe or two probes placed within the cooling system and in particular in the radiator. The probes are designed to complete a circuit from the probe through the coolant to a ground outside of the system and so require a high electrical resistance to operate. If a leak develops and coolant leaves the radiator, the circuit is broken and the driver is given a warning by means of a light or alarm. Such a technique will not work effectively, particularly if there is a slow leak. Even though the general coolant level becomes low, the water pump is still pumping the coolant through the radiator and past the probe so that the sensor indicates that the level is normal when in fact the level is too low and the engine is starting to overheat. If and when substantially all of the coolant leaves the radiator, the warning may then come on, but at this point the engine has overheated and serious damage may have occurred. Moreover, since the sensor triggers on very high resistance, the presence of any coolant on the walls of the radiator may prevent the warning device from ever coming on.